Answer:
Assuming it's a US coin, one way is to weigh it. An unworn silver dime should weigh 2.5 gm, a quarter 6.25 gm, and a half-dollar 12.5 gm. However that wouldn't account for a fake that had been "filled" with a metal having the same density. A jeweler can perform what's called a specific gravity test to tell something about a coin's composition. It involves weighing the coin and comparing the weight to its volume. The density of silver is well-known, so a coin whose density is different from that of silver must have some other metal mixed in, or have no silver at all.